Cluster
Flies
Location: Numerous
locations, but usually in lofts and roof spaces. South-facing
windows and walls often favoured.
Detection: Visual
sightings of large numbers of adults.
There are three main
species of fly collectively known as cluster flies. They are Musca
autumalis, a small fly of about the same size and colour as
the house fly, Pollenia rudis, a larger fly dull brown/grey
in colour, and lastly Dasyhora caynella which is about
house fly size and shiny green/blue in colour.
Biology:
Cluster flies, particularly
Pollenia rudis are very common occurring throughout Great Britain.
The adult flies during the summer months, lay their eggs in the
earth or in animal dung. Permanent areas of grassland are favourite
sites e.g. permanent grazed pasture or parkland as solid cultivation
such as ploughing disrupts the flies breeding cycle. The larval
stage is parasitic, entering earthworms and feeding upon them
until emerging as an adult fly.
Cluster flies migrate
from outdoors into the lofts of houses and farm buildings during
the autumn months causing a nuisance to householders. Obvious
signs of an infestation is a roof space containing a large quantity
of lethargic flies and a quantity of dead flies. Unless the loft
is used for storage purposes or is accessed regularly the flies
will hibernate successfully leaving in early spring dependent
on the weather.
Reasons for control:
Cluster flies are
not damaging to property when they enter buildings in the autumn
purely to hibernate over the cold winter months. As mentioned
above they feed on decaying vegetation and earthworms. Cluster
flies are not to be associated with dead animal bodies, faeces
and the resulting maggots. Fibre glass insulation material in
lofts can look unsightly if covered with the bodies of flies that
have not hibernated successfully although its insulation properties
will not be altered and no damage to the roof structure will occur.
If the loft is home
to a hibernating colony of flies, first floor lighting diffusers
or sunken spot light lenses can become full of dead or dying flies.
This often occurs in houses where the loft area has been converted
into a living room. In most buildings built after 1950, the external
roof covering has an under felt layer. Cluster flies can successfully
hibernate undetected between these two layers. Often cluster flies
can be seen basking on sunny grassland or resting on south facing
walls of buildings. Cluster flies, like birds, return to roof
spaces previously occupied so re-infestation is almost inevitable.
Control/Treatment:
Insecticidal space spray by us
or another pest control company (N.B. if bats are present in your
loft/attic this will not be possible). If you are not in our area
please see the BPCA's web site to locate a pest control company
near you search
BPCA member. Number of visits required
will depend on the time of year the treatment is carried out and
also on weather conditions (mild autumn) as to when flies come
in to hibernate.
The use of fly control units also
works well (N.B. it is not recommended that electric grid machines
are used in loft areas/roof voids, however if you wish to use
this type of machine it is important that these are used with
an extra deep cluster tray and checked on a regular basis). Please
see our online eshop www.hygieneshop.co.uk
for fly killer units which are suitable for controlling cluster
flies.
Below photo shows a glueboard covered in cluster
flies:-
N.B. If bats are present in the
roof space, then it is not recommended that any sort of fly control
is used.
